Semiconductor device and method for manufacturing of the same

ABSTRACT

The present invention provides a semiconductor device including: a base substrate; a first semiconductor layer disposed on the base substrate; first ohmic electrodes disposed on a central region of the first semiconductor layer; a second ohmic electrode having a ring shape surrounding the first ohmic electrodes, on edge regions of the first semiconductor layer; a second semiconductor layer interposed between the first ohmic electrodes and the first semiconductor layer; and a Schottky electrode part which covers the first ohmic electrodes on the central regions, and is spaced apart from the second ohmic electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2009-0084598 filed with the Korea Intellectual Property Office onSep. 8, 2009, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device; and, moreparticularly, to a semiconductor device having a Schottky diodestructure, and a method for manufacturing the same.

2. Description of the Related Art

In general, an active device of semiconductor devices is used toconfigure a circuit, such as an amplifier, a voltage regulator, acurrent regulator, an oscillator, a logic gate, and so on. A diode ofactive devices is widely used as a detecting device, a rectifyingdevice, and a switching device. As for a typical diode, a voltageregulator diode, a variable capacitance diode, a photo diode, a LightEmitting Diode (LED), a zener diode, a gunn diode, a Schottky diode, andso on are exemplified.

The Schottky diode of the exemplified diodes uses Schottky junctiongenerated when a metal comes into contact with semiconductor. TheSchottky diode can implement high-speed switching operation and lowforward voltage driving. The nitride-based semiconductor device like theSchottky diode has a Schottky contact as an anode electrode, and anohmic contact as a cathode electrode. However, in the Schottky diodewith such a structure, there exists a trade-off relation betweensatisfaction of low on-voltage and on-current and reduction of a reverseleakage current. Thus, it is difficult to develop a nitride-basedsemiconductor device capable of operating at a low on-voltage andreducing a reverse leakage current.

SUMMARY OF THE INVENTION

The present invention has been proposed in order to overcome theabove-described problems and it is, therefore, an object of the presentinvention to provide a semiconductor device operable at a low on-voltageand a method for manufacturing the same.

Further, another object of the present invention is to provide asemiconductor device for reducing a reverse leakage current and a methodfor manufacturing the same.

Further, another object of the present invention is to provide asemiconductor device for increasing a breakdown current and a method formanufacturing the same.

Further, another object of the present invention is to provide asemiconductor device having a high forward current and a method formanufacturing the same.

In accordance with one aspect of the present invention to achieve theobject, there is provided a semiconductor device including: a basesubstrate; a first semiconductor layer disposed on the base substrate;first ohmic electrodes disposed on a central region of the firstsemiconductor layer; a second ohmic electrode having a ring shapesurrounding the first ohmic electrodes, on edge regions of the firstsemiconductor layer; a second semiconductor layer interposed between thefirst ohmic electrodes and the first semiconductor layer; and a Schottkyelectrode part which covers the first ohmic electrodes on the centralregions, and is spaced apart from the second ohmic electrode.

The first ohmic electrode has a plurality of ohmic contact pillars withan island-shaped cross section, and the Schottky electrode part and theohmic contact pillars are formed to be in a prominence and depressionstructure in which they are engaged with one another up and down.

The first ohmic electrode includes a plurality of ohmic contact pillarswith an island-shaped cross section, and the ohmic contacts are disposedto be in a grid configuration within the Schottky electrode part.

The first ohmic electrode includes at least one electrode with aring-shaped cross section.

The first ohmic electrode shares a center of the semiconductor layer,and includes first and second electrodes with mutually differentdiameters.

The first ohmic electrodes are formed of the same metallic material asthe Schottky electrode part, and the Schottky electrode part includes:first bonding portions bonded to the second semiconductor layer tothereby come into ohmic contact with the second semiconductor layer, andsecond bonding portions bonded to the first semiconductor layer tothereby come into Schottky contact with the first semiconductor layer.

The first semiconductor layer comprises protrusions protruded upward,and the second semiconductor layer is disposed on the protrusions.

The first semiconductor layer includes: a lower layer adjacent to thebase substrate; and an upper layer having a lower impurity concentrationthan that of the lower layer, and the second semiconductor layer has ahigher impurity concentration than that of the upper layer.

The first ohmic electrodes are bonded to the second semiconductor layeron the central region to thereby come into ohmic contact with the secondsemiconductor layer, the second ohmic electrode is bonded to thesemiconductor layer on the edge regions to thereby come into ohmiccontact with the semiconductor layer, and the Schottky electrode part isbonded to the second semiconductor layer around the first ohmicelectrodes to thereby come into Schottky contact with the secondsemiconductor layer.

The Schottky electrode part is extended to inside of the semiconductorlayer, and the Schottky electrode part has a bottom surface with aheight lower than that of the top surface of the second semiconductorlayer.

The second ohmic electrode is extended to inside of the firstsemiconductor layer.

The semiconductor device further includes a field plate disposed betweenthe first ohmic electrodes and the second ohmic electrode.

The internal side portions of the filed plate are covered by theSchottky electrode, and the external side portions of the filed platepartially cover an internal side of the top part of the second ohmicelectrode, and central portion of the field plate is exposed.

In accordance with other aspect of the present invention to achieve theobject, there is provided a semiconductor device including: a basesubstrate; a first semiconductor layer disposed on the base substrate;first ohmic electrodes which are disposed on a central region of thefirst semiconductor layer and have a plurality of ohmic contact pillarswith an island-shaped cross section; a second ohmic electrode disposedon the edge regions of the first semiconductor layer; and a Schottkyelectrode part which includes first bonding portions bonded to the firstohmic contact pillars and second bonding portions bonded to the firstsemiconductor layer, wherein a depletion region is provided to permit orto block a current flow to the second ohmic electrode from the firstohmic electrodes and the Schottky electrode part, the depletion regionbeing generated within the first semiconductor layer when thesemiconductor layer is bonded to the second bonding portions.

The Schottky electrode part is engaged with the first ohmic contactpillars to thereby achieve a prominence and depression structure.

When the semiconductor device is driven at a forward voltage equal to orhigher than an on-voltage of the Schottky diode, the depletion region isprovided to permit a current flow to the second ohmic electrode from theSchottky electrode part and the first ohmic electrodes.

When the semiconductor device is driven at a forward voltage lower thanthe on-voltage of the Schottky diode, the depletion region is providedto block a current flow to the second ohmic electrode from the Schottkyelectrode part.

When the semiconductor device is driven at a reverse voltage, thedepletion region is provided to block a current flow to the second ohmicelectrode from the Schottky electrode part and the first ohmicelectrodes.

In accordance with other aspect of the present invention to achieve theobject, there is provided a method for manufacturing a semiconductordevice including the steps of: preparing a base substrate; forming afirst semiconductor layer on the base substrate; forming a secondsemiconductor layer on a partial region of the first semiconductorlayer; forming first ohmic electrodes on a top part of the secondsemiconductor layer; forming a second ohmic electrode surrounding thefirst ohmic electrodes on edge regions of the first semiconductor layer;and forming a Schottky electrode part which covers the first ohmicelectrodes on the central region of the semiconductor layer.

The step of forming the first ohmic electrodes includes a step offorming a plurality of ohmic contact pillars with an island-shaped crosssection, and the ohmic contact pillars have recesses formed on regionsremaining after excluding regions of the first semiconductor layer wherethe first ohmic electrodes are to be formed.

The step of forming the first ohmic electrodes comprises a step offorming the first and second electrodes provided to be in an annual ringconfiguration on the first semiconductor layer, and the first and secondelectrodes have recesses formed on regions, remaining after excludingregions of the first semiconductor layer where the first ohmicelectrodes are to be formed.

The recess has a bottom surface with a height lower than that of thebottom surface of the second semiconductor layer.

The step of forming the first semiconductor layer includes the steps of:forming a lower layer having a high impurity concentration on the basesubstrate; and forming an upper layer having an impurity concentrationlower than that of the lower layer, and the step of forming the secondsemiconductor layer comprises a step of forming a semiconductor filmhaving an impurity concentration higher than that of the upper layer.

The step of forming the upper layer includes a step of: performing anepitaxial-growth process which uses the lower layer as a seed layer, andthe step of forming the second semiconductor layer comprises a step ofperforming any one of an epitaxial-growth process which uses the upperlayer as a seed layer, and a deposition process.

The method further includes a step of forming a field plate on the firstsemiconductor layer between the Schottky electrode part and the secondohmic electrode.

The step of forming the second ohmic electrode includes a step offorming a metal film, which has external side portions partiallycovering a top part of the second ohmic electrode and a part of internalside portions covered by the Schottky electrode part.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of the embodiments, taken in conjunction withthe accompanying drawings of which:

FIG. 1 is a view showing a semiconductor device in accordance with oneembodiment of the present invention;

FIG. 2 is a cross-sectional view taken along a line I-I′ of FIG. 1;

FIGS. 3A to 3C are views showing operation states of the semiconductordevice shown in FIG. 1, respectively;

FIGS. 4A to 4C are views showing methods for manufacturing thesemiconductor device 100 in accordance with an embodiment of the presentinvention, respectively;

FIG. 5 is a view showing one modified example of a semiconductor devicein accordance with one embodiment of the present invention;

FIG. 6 is a view showing other modified example of a semiconductordevice shown in accordance with one embodiment of the present invention;

FIG. 7 is a view showing other modified example of a semiconductordevice shown in accordance with one embodiment of the present invention;

FIG. 8 is a view showing other modified example of a semiconductordevice shown in accordance with one embodiment of the present invention;

FIG. 9 is a view showing other modified example of a semiconductordevice shown in accordance with one embodiment of the present invention;

FIG. 10 is a cross-sectional view taken along a line II-II′ of FIG. 9;

FIG. 11 is a plane-view showing a semiconductor device in accordancewith other embodiment of the present invention;

FIG. 12 is a cross-sectional view taken along a line III-III′ of FIG.11;

FIGS. 13A to 13C are views showing operation states of the semiconductordevice shown in FIGS. 11 and FIG. 12, respectively;

FIGS. 14A to 14D are views showing methods for manufacturing thesemiconductor device 200 in accordance with other embodiment of thepresent invention, respectively;

FIG. 15 is a view showing one modified example of a semiconductor devicein accordance with other embodiment of the present invention;

FIG. 16 is a view showing other modified example of a semiconductordevice shown in accordance with other embodiment of the presentinvention; and

FIG. 17 is a cross-sectional view taken along a line IV-IV′ of FIG. 16.

DETAILED DESCRIPTION OF THE PREFERABLE EMBODIMENTS

The invention now will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likereference numerals refer to like elements throughout.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

Preferred embodiments of the invention will be described below withreference to cross-sectional views, which are exemplary drawings of theinvention. The exemplary drawings may be modified by manufacturingtechniques and/or tolerances. Accordingly, the preferred embodiments ofthe invention are not limited to specific configurations shown in thedrawings, and include modifications based on the method of manufacturingthe semiconductor device. For example, an etched region shown at a rightangle may be formed in the rounded shape or formed to have apredetermined curvature. Therefore, regions shown in the drawings haveschematic characteristics. In addition, the shapes of the regions shownin the drawings exemplify specific shapes of regions in an element, anddo not limit the invention.

Hereinafter, a detailed description will be given of a semiconductordevice and a method for manufacturing the same in accordance withembodiments of the present invention, with reference to accompanyingdrawings.

FIG. 1 is a view showing a semiconductor device in accordance with oneembodiment of the present invention, and FIG. 2 is a cross-sectionalview taken along a line I-I′ of FIG. 1.

Referring to FIGS. 1 and 2, the semiconductor device 100 may include abase substrate 110, a first semiconductor layer 120, an ohmic electrodepart 130, and a Schottky electrode part 140.

The base substrate 110 may be a plate used for formation of thesemiconductor device having a Schottky diode structure. For example, thebase substrate 110 may be a semiconductor substrate. As for the basesubstrate 110, at least one of a silicon substrate, a silicon carbidesubstrate, and a sapphire substrate may be exemplified.

The first semiconductor layer 120 may be disposed on the base substrate110, and may provide a current flow path to inside thereof. For example,the first semiconductor layer 120 may include a lower layer 122 and anupper layer 124. The lower layer 122 may be a semiconductor layer havinga higher impurity concentration than that of the upper layer 124. Forexample, the lower layer 122 may be an N-type semiconductor film havinga relatively high impurity concentration, and the upper layer 124 may bean N-type semiconductor film having a relatively low impurityconcentration. Meanwhile, a buffering film (not shown) may be furtherprovided between the base substrate 110 and the lower layer 122 so as tosolve problems caused by lattice mismatch generated between the basesubstrate 110 and the lower layer 122.

The ohmic electrode part 130 may include first ohmic electrodes 132 anda second ohmic electrode 134. The first ohmic electrodes 132 may bedisposed on a central region A1 of the first semiconductor layer 120.The first ohmic electrode 132 may include at least one of ohmic contactpillars having an island-shaped cross section. For example, the firstohmic electrode 132 may have a plurality of ohmic contact pillars withan island-shaped cross section. Each of the first ohmic contact pillarsmay have a rectangular-shaped cross section. However, the first ohmiccontact pillars may have a circular cross section. The ohmic contactpillars may be disposed to be in a grid configuration as shown in FIG.1.

The second ohmic electrode 134 may be formed on edge regions A2 of theupper layer 124. The second ohmic electrode 134 may be disposed on edgeregions A2 of the upper layer 124 so that it can surround the firstohmic electrodes 132. Thus, the second ohmic electrode 134 may begenerally formed in a ring shape. Also, the second ohmic electrode 134may be disposed to be spaced apart from the first ohmic electrodes 132.

Meanwhile, the second semiconductor layer 128 may be interposed betweenthe first semiconductor layer 120 and the first ohmic electrodes 132.The second semiconductor layer 128 may be a semiconductor film having arelatively higher impurity concentration than that of the firstsemiconductor layer 120. For example, the second semiconductor layer 128may be an N-type semiconductor film having a relatively higher impurityconcentration than that of the first semiconductor layer 120. The firstohmic electrodes 132 are bonded to the second semiconductor layer 128 tothereby come into ohmic contact with the second semiconductor layer 128.

The Schottky electrode part 140 may be provided to cover the first ohmicelectrodes 132. For example, the Schottky electrode part 140 may beprovided on the central region A1 of the upper layer 124 so that it canentirely cover all ohmic contact pillars of the first ohmic electrodes132. Thus, the Schottky electrode part 140 and the ohmic contact pillarsmay have a prominence and depression structure in which they are engagedwith each other up and down. The Schottky electrode part 140 may havefirst bonding portions 142 bonded to the first ohmic electrodes 132, andsecond bonding portions 144 bonded to the first semiconductor layer 120adjacent to the first ohmic electrodes 132. A depletion region DR may beformed within the first semiconductor layer 120 adjacent to the secondbonding portions 144.

Herein, the Schottky electrode part 140 may be extended to inside of thefirst semiconductor layer 120. For example, the second bonding portions144 of the Schottky electrode part 140 may be extended to inside of theupper layer 124, and may be disposed to be spaced apart from the lowerlayer 122. Thus, the Schottky electrode part 140 may have a bottomsurface height lower than that of a top surface of the secondsemiconductor layer 128. To this end, the recesses 126 may be providedin the upper layer 124 of the first semiconductor layer 120. Therecesses 126 may be formed by depressing regions excluding regions wherethe first ohmic electrodes 132 are formed on the upper layer 124. Thus,the upper layer 124 may have protrusions 125 having an upward protrudedstructure formed on the upper layer 124, and the first ohmic electrodes132 may be disposed on the protrusions 125.

The semiconductor device 100 may further include a field plate 150. Thefield plate 150 may be disposed on the first semiconductor layer 120between the second ohmic electrode 134 and the Schottky electrode part140. In this case, a part of external side portions 152 of the fieldplate 150 may be provided to cover internal corners of a top surface ofthe second ohmic electrode 134, and a part of internal side portions 154of the field plate 150 may be provided to be covered by the edgeportions 144 of the Schottky electrode part 140. The field plate 150 canprovide an effect of distributing an electric field concentrated oncorner portions of the Schottky electrode part 140 and the ohmicelectrode part 130.

In the semiconductor device 100 having the same structure, each of thefirst ohmic electrodes 132 are bonded to the second semiconductor layer128 in the central region A1 to thereby come into ohmic contact witheach other. The second ohmic electrode 134 is bonded to the upper layer124 in the edge regions A2 to thereby come into ohmic contact with eachother. The Schottky electrode part 140 is bonded to the upper layer 124of the central region A1 adjacent to the first ohmic electrodes 132 tothereby come into Schottky contact with each other. Herein, the Schottkyelectrode part 140 may be used as an anode electrode, and the secondohmic electrode 134 may be used as a cathode electrode.

Meanwhile, the ohmic electrode part 130 and the Schottky electrode part140 may be formed of various materials. For example, the first ohmicelectrodes 132 and the second ohmic electrode 134 may be formed of thesame metallic material, and the Schottky electrode part 140 may beformed of metallic material different from those of the first and secondohmic electrodes 132 and 134. For example, the first and second ohmicelectrodes 132 and 134 may be formed of a metallic material composed ofat least one metal element of Al, Mo, Au, Ni, Pt, Ti, Pd, Ir, Rh, Co, W,Ta, Cu, and Zn. On the contrary, the Schottky electrode part 140 may beformed of a material composed of one or more metal elements differentfrom that of the ohmic electrode part 130.

Continuously, a detailed description will be given of various operationstates of the semiconductor device in accordance with one embodiment ofthe present invention having been described with reference to FIGS. 1and 2.

FIGS. 3A to 3C are views showing operation states of the semiconductordevice shown in FIG. 1, respectively. FIG. 3A is a view showing anoperation state of the semiconductor device when driven at a forwardvoltage equal to or higher than an on-voltage of the Schottky diode.Referring to FIG. 3A, when the semiconductor device 100 in accordancewith one embodiment of the present invention is driven at a firstforward voltage equal to or higher than the on-voltage of the Schottkydiode, a depletion region (DR1) generated where the first semiconductorlayer 120 and the Schottky electrode part 140 are joined together may berelatively reduced. Thus, in the semiconductor device 100, a current mayflow through a first current path CP1 and a second current path CP2,wherein the first current path CP1 passes through the firs semiconductorlayer 120 from the second bonding portions 144 of the Schottky electrodepart 140, and the second current path CP2 passes through the first andsecond semiconductor layers 120 and 128 from the first ohmic electrodes132. In this case, since forward currents of the semiconductor device100 are increased, it is possible to operate the semiconductor device100 even at a low on-voltage.

FIG. 3B is a view showing an operation state of the semiconductor devicewhen driven at a forward voltage lower than an on-voltage of theSchottky diode. Referring to FIG. 3B, when the semiconductor device 100in accordance with one embodiment of the present invention is driven ata second forward voltage lower than the on-voltage of the Schottkydiode, a depletion region DR2 generated where the second semiconductorlayer 120 and the Schottky electrode part 140 are joined together may bemore expanded than the depletion region DR1 corresponding to a casewhere the semiconductor device 100 is driven at the first forwardvoltage as described in FIG. 3A. Such the expanded depletion region DR2may be wide enough to block a current flow between the firstsemiconductor layer 120 and the Schottky electrode part 140. However,the second forward voltage may be controlled such that the depletionregion DR2 fails to block the second current path CP2. Thus, in thesemiconductor device 100, a current may flow through the second currentpath CP2 alone.

FIG. 3C is a view showing an operation state of the semiconductor devicewhen driven at a reverse voltage. Referring to FIG. 3C, when thesemiconductor device 100 is driven at the reverse voltage, a depletionregion D3 may be more expanded to block the first and second currentpaths, indicated by reference numerals CP1 and CP2 of FIG. 3A, incomparison with the depletion region DR2 shown in FIG. 3B. Such thedepletion region DR3 blocks all current flows passing through the firstand second current paths CP1 and the CP2.

As described above, when the semiconductor device 100 is driven in theforward direction, a current may flow to the second ohmic electrode 134by the first ohmic electrodes 132 positioned below the Schottkyelectrode part 140 even in a state where the driving voltage is lowerthan the on-voltage of the Schottky diode, simultaneously while thecurrent may flow through the first ohmic electrodes 132 and the Schottkyelectrode part 140 in a state where the driving voltage is higher thanthe on-voltage of the Schottky diode. Thus, since the semiconductordevice 100 may increase forward currents, it can be operated even at alow driving voltage. Also, when the semiconductor device 100 is drivenin the reverse direction, the depletion region DR3 generated by theSchottky electrode part 140 blocks a current flow passing through thefirst and second semiconductor layers 120 and 128, thereby stablyblocking a current flow.

Hereinafter, a description will be given of a method for manufacturingthe semiconductor device in accordance with one embodiment of thepresent invention. Herein, the repeated description for thesemiconductor device will be omitted or simplified.

FIGS. 4A to 4C are views showing methods for manufacturing thesemiconductor device 100 in accordance with an embodiment of the presentinvention, respectively.

Referring to FIG. 4A, the base substrate 110 may be prepared. Forexample, a step of preparing the base substrate 110 may include a stepof preparing a semiconductor substrate. The step of preparing the basesubstrate 110 may include a step of preparing at least one of a siliconsubstrate, a silicon carbide substrate, and a sapphire substrate.

A lower layer 122 and a pre-upper layer 123 may be sequentially formedon the base substrate 110. The step of forming the first semiconductorlayer 120 may be achieved by epitaxial-growing the lower layer 122 byusing the base substrate 110 as a seed layer, and then epitaxial-growingthe pre-upper layer 123 by using the lower layer 122 as a seed layer.

The second semiconductor layer 128 may be formed. For example, a step offorming the second semiconductor layer 128 may include a step of formingthe semiconductor film having a relatively higher impurity concentrationthan that of the pre-upper layer 123, on the pre-upper layer 123. Forexample, the step of forming the second semiconductor layer 128 mayinclude a step of epitaxial-growing the semiconductor material havingimpurity concentration higher than that of the upper layer 124 by usingthe upper layer 124 as a seed layer. As for another example, the step offorming the pre-second semiconductor layer may include a step ofdepositing the semiconductor film having an impurity concentrationhigher than that of the upper layer 124, on the upper layer 123.

On the pre-upper layer 123 and the pre-second semiconductor layer, therecesses 126 may be formed. The step of forming the recesses 126 mayinclude a step of: forming the first photoresist pattern PR1 exposingthe first metal film of regions excluding regions where the first ohmicelectrodes, indicated by reference numeral 132 of FIG. 4C, are to beformed, as well as the edge regions A2, on a resulting material formedwith the pre-second semiconductor layer 128; a step of performing anetching process which exposes the pre-upper layer 123 by using the firstphotoresist pattern PR1 as an etching mask; and a step of removing thefirst photoresist pattern PR1. Thus, on the pre-upper layer 123, theprotrusions 125 extended from the top surface are provided, and thesecond semiconductor layer 128 may selectively remain on the protrusions125.

As for an epitaxial growth process for forming the pre-upper layer 123and the pre-second semiconductor layer, at least one of a molecular beamepitaxial growth process, an atomic layer epitaxial growth process, aflow modulation organometallic vapor phase epitaxial growth process, aflow modulation organometallic vapor phase epitaxial growth process, anda hybrid vapor phase epitaxial growth process may be used. Furthermore,as for another process for forming the pre-upper layer 123 and thepre-second semiconductor layer, any one of a chemical vapor depositionprocess and a physical vapor deposition process may be used.

Referring to FIG. 4B, edge regions A2 of the first semiconductor layer120 may be etched. For example, a second photoresist pattern PR2 forexposing edge regions A2 may be formed on the resulting material formedwith the recesses 126, and then an etching process may be performedwhere the second photoresist pattern PR2 is used as an etching mask.Thus, the first semiconductor layer 120 may be formed which includes alower layer 122, and the upper layer 124, wherein the lower layer 122covers all surfaces of the base substrate 110 and the upper layer 124has a depression 124 a exposing the lower layer 122 on the edge regionsA2 of the first semiconductor layer 120.

Referring to FIG. 4C, the ohmic electrode part 130 may be formed on thesemiconductor layer 120. For example, a first metal film may be formedon the upper layer 124. A step of forming the first metal film mayinclude a step of forming a metal film, which is composed of at leastone of Au, Ni, Pt, Ti, Al, Pd, Ir, Rh, Co, W, Mo, Ta, Cu, and Zn, in aconformal manner, on the upper layer 124. Thereafter, a thirdphotoresist pattern PR3 exposing the first metal film on the regions,excluding regions where the first ohmic electrodes 132 are to be formedamong the middle regions A3, and the middle region A1, may be formed onthe first metal film. Then, after the first metal film is etched byusing the third photoresist pattern PR3 as an etching mask, it ispossible to remove the third photoresist pattern PR3. Thus, the firstohmic electrodes having a plurality of ohmic contact pillars disposed tobe in a lattice configuration on the central region A1, and the secondohmic electrode 134 having a ring shape formed along the edge regions A2may be formed on the first semiconductor layer 120. Herein, since thefirst ohmic electrodes 132 and the second ohmic electrode 134 aresimultaneously formed in the same etching process, they may be formed ofthe same metallic material. For example, the first ohmic electrodes 132and the second ohmic electrode 134 may be formed in an in-situ scheme.Meanwhile, a process of planarizing the first metal film may be addedbefore the first metal film is etched.

Referring to FIG. 4D, the field plate 150 may be formed. For example, aninsulating film which covers all surfaces of the resulting materialformed with the ohmic electrode part 130 may be formed in a conformalmanner, and the fourth photoresist pattern PR4 may be formed on theinsulating film. The fourth photoresist pattern PR4 can expose remainingregion B1 including a part of the edge regions A2 and a part of themiddle regions A3 of the first semiconductor layer 120. Then, theinsulating film is etched by using the fourth photoresist pattern PR4 asan etching mask, and then the fourth photoresist pattern PR4 may beremoved. The field plate 150 may be formed that covers the second ohmicelectrode 134 and the first semiconductor layer 120 exposed to themiddle regions A2. In this case, external side portions 152 of the fieldplate 150 may be provided to cover a part of the edges of the topsurface of the second ohmic electrode 134. In addition, internal sideportions 154 of the field plate 150 may be provided to be spaced apartfrom the first ohmic electrodes 132 on the middle regions A2.

Referring to FIG. 4E, the Schottky electrode part 140 may be formed thatcovers the first ohmic electrodes 132. For example, the step of formingthe Schottky electrode part 140 may include a step of forming the secondmetal film that covers the resulting material formed with ohmicelectrode part 130, and a step of forming the fifth photoresist patternPR5 on the second metal film. The fifth photoresist pattern PR5 canexpose a part of the edge regions A2 and the middle regions A3 of thefirst semiconductor layer 120. Thereafter, it is possible to perform anetching process which uses the fifth photoresist pattern PR5 as anetching mask, thereby forming the Schottky electrode part 140 which isspaced apart from the ohmic electrode 134 and entirely covers the firstohmic electrodes 132. In this case, the Schottky electrode part 140 maybe formed so that it can cover internal side portions 154 of the fieldplate 150. Thus, it is possible to distribute an electric fieldconcentrated on external corners of the Schottky electrode part 140.

Hereinafter, a description will be given of various modified examples ofthe semiconductor device in accordance with other embodiment of thepresent invention. The repeated description for the same componentsbetween the above-described semiconductor device and semiconductordevices in accordance with various modified embodiments will be omittedor simplified. Since those skilled in the art can analogize operationprocesses of the modified examples to be described from the operationstates of the semiconductor device having been described with referenceto FIGS. 3A and 3C, the description for operation processes of themodified examples will be omitted. Also, since those skilled in the artcan analogize manufacturing methods of the modified examples to bedescribed from the manufacturing methods of the semiconductor devicehaving been described with reference to FIGS. 4A and 4E, the descriptionfor manufacturing methods of the modified examples will be omitted.

FIG. 5 is a view showing one modified example of the semiconductordevice in accordance with one embodiment of the present invention.Referring to FIG. 5, the semiconductor device 100 a in accordance withone modified embodiment of the present invention may include a basesubstrate 110, a first semiconductor layer 120 a, a second semiconductorlayer 128, an ohmic electrode part 130, a Schottky electrode part 140,and a field plate 150.

The first semiconductor layer 120 a may include a lower layer 122 and anupper layer 124 a, wherein the lower layer 122 is disposed to beadjacent to the base substrate 110, and the upper layer 124 a is formedon lower layer 122. The ohmic electrode part 130 may be disposed on theupper layer 124 a. The ohmic electrode part 130 may include the firstohmic electrodes 132 which are provided with a plurality of ohmiccontact pillars with an island-shaped cross section on the centralregion A1, and a second ohmic electrode 134 having a ring shape on edgeregions thereof. The Schottky electrode part 140 may be formed toentirely cover the first ohmic electrodes 132. Thus, the ohmic electrodepillars of the first ohmic electrodes 132 are engaged with the Schottkyelectrode part 140 to thereby achieve a prominence and depressionstructure. The field plate 150 may be provided that mostly covers cornerportions of the Schottky electrode part 140 and the second ohmicelectrode 134 on the middle regions A3.

Meanwhile, the ohmic electrode part 130 may be disposed on the first andsecond protrusions 125 and 127 formed on the first semiconductor layer120. For example, the first ohmic electrodes 132 may be disposed on theprotrusions 125 extended upward from the upper layer 124 a in thecentral region A1. The second ohmic electrode 134 may be disposed on thesecond protrusions 127 extended upward from the upper layer 124 a in theedge regions A2. Herein, the second semiconductor layer 128 may beinterposed between the first protrusions 125 and the first ohmicelectrodes 132, and between the second protrusions 127 and the secondohmic electrode 134. The semiconductor device 100 a may have a structurein which the second ohmic electrode 134 is disposed on the secondprotrusions 127 of the first semiconductor layer 120 a. In this case,metal films for formation of the first semiconductor layer 120, thesecond semiconductor layer 128, and the ohmic electrode part 130 on thebase substrate 110 may be sequentially formed, and then a photoresistetching process may be performed once, thereby forming the first andsecond ohmic electrodes 132 and 134 at the same time. Thus, a method formanufacturing the semiconductor device 100 a may be relativelysimplified.

FIG. 6 is a view showing other modified example of the semiconductordevice in accordance with one embodiment of the present invention.Referring to FIG. 6, the semiconductor device 100 b in accordance withone modified embodiment of the present invention may include a basesubstrate 110 b, a second semiconductor layer 128, an ohmic electrodepart 130 b, a Schottky electrode part 140, and a field plate 150. Theohmic electrode part 130 b may be deposed on the second semiconductorlayer 128 interposed on the base substrate 110 b. The ohmic electrodepart 130 b may include the first ohmic electrodes 132 which are providedwith a plurality of ohmic contact pillars with island-shaped crosssections on the central region A1 of the base substrate 110 b, and thesecond ohmic electrode 134 having a ring shape formed along the edgeregions A2 of the base substrate 110 b. The Schottky electrode part 140covers the first ohmic electrodes 132 to thereby achieve a prominenceand depression structure in which the Schottky electrode part 140 isengaged with the ohmic electrode pillars up and down. The field plate150 may be disposed between the second ohmic electrode 134 and theSchottky electrode part 140 on the middle regions A3 of the basesubstrate 110 b.

Meanwhile, the base substrate 110 b may be a semiconductor substrate.For example, the base substrate 110 b may be an N-type semiconductorfilm having a relatively lower impurity concentration than that of thesecond semiconductor layer 128. In addition, the base substrate 110 bmay be formed of a material with a high resistivity. For example, thebase substrate 110 b may be an N-type semiconductor film having a lowimpurity concentration, and the second semiconductor layer 128 may be anN-type semiconductor film having a relatively higher impurityconcentration than that of the base substrate 110 b.

Unlike the above-described semiconductor devices 100 and 100 a, thesemiconductor device 100 b provides a base substrate 110 correspondingto a semiconductor film having a low impurity concentration, so that thesemiconductor device 100 b is not required to have a separatesemiconductor layer between the base substrate 110 and the secondsemiconductor layer 128 formed thereon. For example, in a method formanufacturing the semiconductor device 100 b, a process (e.g.,epitaxial-growth process, chemical vapor deposition process, and aphysical vapor deposition, and so on) of forming a separatesemiconductor layer (e.g., first semiconductor layers 120 and 120 ashown in FIGS. 2 and 5) may be omitted.

FIG. 7 is a view showing other modified example of the semiconductordevice in accordance with one embodiment of the present invention.Referring to FIG. 7, the semiconductor device 100 c may include a basesubstrate 110, a first semiconductor layer 120, an ohmic electrode part130 c, a Schottky electrode part 140, and a field plate 150. The basesubstrate 110 may have a front surface, and a rear surface opposite tothe front surface. The first semiconductor layer 120 may include anupper layer 124 and a lower layer 122 sequentially stacked on the basesubstrate 110, wherein the upper layer 124 has a lower impurityconcentration than that of the lower layer 122. The ohmic electrode part130 c may be disposed on the base substrate 110 after the secondsemiconductor layer 128 with a higher impurity concentration that of theupper layer 124 is interposed. The ohmic electrode part 130 c mayinclude the first ohmic electrodes 132 which are provided with aplurality of ohmic contact pillars with island-shaped cross sections onthe central region A1 of the base substrate 110 b. The Schottkyelectrode part 140 covers the first ohmic electrodes 132 to therebyachieve a prominence and depression structure in which the Schottkyelectrode part 140 is engaged with the ohmic electrode pillars up anddown. The field plate 150 may be disposed between the second ohmicelectrode 134 c and the Schottky electrode part 140 on the middleregions A3 of the base substrate 110 b.

Meanwhile, the ohmic electrode part 130 b may further include a secondohmic electrode 134 c disposed on a rear surface of the base substrate110. The second ohmic electrode 134 c may be formed of the same metallicmaterial as the first ohmic electrodes 132. The second ohmic electrode134 c may be used as a cathode electrode of the semiconductor device 100c. In this case, the Schottky electrode part 140 may be used an anodeelectrode of the semiconductor device 100 c. The semiconductor device100 c has a structure in which the first ohmic electrodes 132 aredisposed on the front surface of the base substrate 110 and the secondohmic electrode 134 c is disposed on the rear surface of the basesubstrate 110. Thus, within the semiconductor device 100 c, there isgenerated a structure in which a vertical current flow in up and downdirections.

FIG. 8 is a view showing other modified example of the semiconductordevice in accordance with one embodiment of the present invention.Referring to FIG. 8, the semiconductor device 100 d may include a basesubstrate 110, a first semiconductor layer 120, an ohmic electrode part130 d, a Schottky electrode part 140 d, and a field plate 150 d. Thefirst semiconductor layer 120 may include a lower layer 122 and an upperlayer 124 sequentially stacked on the front surface of the basesubstrate 110, wherein the upper layer 124 has a lower impurityconcentration than that of the lower layer 122. The ohmic electrode part130 d may be disposed on edge regions A2 of the first semiconductorlayer 120. The Schottky electrode part 140 d may be disposed on thecentral region A3 of the first semiconductor layer 120. Herein, theprotrusions 125 protruded upward from the top surface of the firstsemiconductor layer 120 may be formed on the central region A1 of thefirst semiconductor layer 120, and the second semiconductor layer 128having a higher impurity concentration than that of the upper layer 124may be disposed on the protrusions 125. Thus, a pillar configuration maybe achieved between the protrusions 125 and the second semiconductorlayer 128. The Schottky electrode part 140 d covers the central regionA1 to thereby achieve a prominence and depression structure in whichthey are engaged with one another up and down. The field plate 150 maybe disposed between the second ohmic electrode 134 and the Schottkyelectrode part 140 on the middle regions A3 of the base substrate 110 b.

In the semiconductor device 100 d with the same structure, the Schottkyelectrode part 140 d may have first bonding portions 142 d bonded to thesecond semiconductor layer 128, and second bonding portions 144 d bondedto the first semiconductor layer 120. Herein, the first bonding portions142 d come into ohmic contact with the second semiconductor layer 128,and the second bonding portions 144 d come into Schottky contact withthe upper layer 124 of the first semiconductor layer 120. Thesemiconductor device 100 d is provided with the Schottky electrode part140 d, thereby performing functions of a Schottky diode and an ohmicdiode. Thus, the central region A1 may have a structure in which thereis no separate ohmic electrode within the Schottky electrode part 140 d.Thus, it is possible to form the semiconductor 100 d which can performthe operations described with reference to FIGS. 3A to 3C only through aprocess of forming the Schottky electrode part 140 d which covers theprotrusions 125 and the second semiconductor layer 128, without havingto perform a process of forming a separate ohmic electrode on theprotrusions 125 of the central region A1 in a method for manufacturingthe semiconductor device 100 d.

FIG. 9 is a view showing other modified example of a semiconductordevice in accordance with one embodiment of the present invention, andFIG. 10 is a cross-sectional view taken along a line II-II′ of FIG. 9.

Referring to FIGS. 9 and 10, the semiconductor device 100 e may includea base substrate 110, a first semiconductor layer 120, an ohmicelectrode part 130 e, a Schottky electrode part 140, and a field plate150. The first semiconductor layer 120 may include a lower layer 122 andan upper layer 124 sequentially stacked on the front surface of the basesubstrate 110, wherein the upper layer 124 has a lower impurityconcentration than that of the lower layer 122. The ohmic electrode part130 e may include a first ohmic electrode 133 disposed on the centralregion A1 of the first semiconductor layer 120 and the second ohmicelectrode 134 disposed on the edge regions A2 of the first semiconductorlayer 120. The Schottky electrode part 140 covers the first ohmicelectrode 133 on the central region A1 to thereby achieve a prominenceand depression structure in which they are engaged with one another upand down. The field plate 150 may be disposed on the middle regions A3.

Meanwhile, each of the first ohmic electrodes 133 may have a ring shapebased on the center 111 of the first semiconductor layer 120. Forexample, the first ohmic electrodes 133 may include a first electrode133 a and a second electrode 133 b. The first electrode 133 a and asecond electrode 133 b have a ring shape sharing the center 111 of thesemiconductor layer 120, and the second electrode 133 b may have adiameter bigger than that of the first electrode 133 a. Thus, the firstohmic electrode 133 and the second ohmic electrode 134 are formed to bein an annual ring configuration on the first semiconductor layer 120.The second ohmic electrode 134 may have a ring shape based on the center111 of the semiconductor layer 120. The second ohmic electrode 134 mayhave a ring shape surrounding the first ohmic electrode 133 on the edgeregions A2.

Hereinafter, a detailed description will be given of a semiconductordevice and a method for manufacturing the same in accordance with otherembodiments of the present invention.

FIG. 11 is a plane-view showing a semiconductor device in accordancewith other embodiment of the present invention, and FIG. 12 is across-sectional view taken along a line III-III′ of FIG. 11.

Referring to FIGS. 11 and 12, the semiconductor device 200 may include abase substrate 212, a first semiconductor layer 220, an ohmic electrodepart 230, and a Schottky electrode part 240. The base substrate 212 maybe a plate used for formation of the semiconductor device having aSchottky diode structure. For example, the base substrate 212 may be asemiconductor substrate. As for the base substrate 212, at least one ofa silicon substrate, a silicon carbide substrate, and a sapphiresubstrate may be exemplified.

The first semiconductor layer 220 may be disposed on the base substrate212, and may provide a current flow path to inside thereof. For example,the first semiconductor layer 220 may include a lower layer 222 and anupper layer 224. The lower layer 222 may be a semiconductor layer havinga higher impurity concentration than that of the upper layer 224. Forexample, the lower layer 222 may be an N-type semiconductor film havinga relatively high impurity concentration, and the upper layer 224 may bean N-type semiconductor film having a relatively low impurityconcentration.

Meanwhile, a buffering film (not shown) may be further provided betweenthe base substrate 212 and the lower layer 222 so as to solve problemscaused by lattice mismatch generated between the base substrate 212 andthe lower layer 222.

The ohmic electrode part 230 may include first ohmic electrodes 232 anda second ohmic electrode 234. The first ohmic electrodes 232 may bedisposed on a central region A1 of the front surface 222 a of the firstsemiconductor layer 220. The first ohmic electrode 232 may include atleast one of ohmic contact pillars having an island-shaped crosssection. For example, the first ohmic electrode 232 may have a groupcomposed of a plurality of ohmic contact pillars with an island-shapedcross section. Each of the first ohmic contact pillars may have arectangular-shaped cross section. Also, the first ohmic contact pillarsmay have a circular cross section. The ohmic contact pillars may bedisposed to be in a grid configuration, as shown in FIG. 1. Meanwhile,the second ohmic electrode 234 may be disposed on the central region A1of the rear surface opposite to the front surface 222 a of the firstsemiconductor layer 220. The second ohmic electrode 234 may be providedto directly be in contact with the lower layer 222. To this end, atrench 212 a for exposing the rear surface 222 b of the lower layer 222may be formed on the base substrate 212.

The Schottky electrode part 240 may be provided to cover the first ohmicelectrodes 232. For example, the Schottky electrode part 240 may beprovided so that it can entirely cover all ohmic contact pillars of thefirst ohmic electrodes 232. Thus, the Schottky electrode part 240 andthe ohmic contact pillars may have a prominence and depression structurein which they are engaged with each other up and down. The Schottkyelectrode part 240 may have first bonding portions 242 bonded to thefirst ohmic electrodes 232, and second bonding portions 244 bonded tothe first semiconductor layer 220 adjacent to the second ohmicelectrodes 232. A depletion region DR may be formed within the firstsemiconductor layer 220 adjacent to the second bonding portions 244.

Herein, the Schottky electrode part 240 may be extended to inside of thefirst semiconductor layer 220. For example, the second bonding portions244 of the Schottky electrode part 240 may be extended to inside of theupper layer 224 of the first semiconductor layer 220, and may bedisposed to be spaced apart from the lower layer 222. Thus, the Schottkyelectrode part 240 may have a bottom surface with a height lower thanthat of a top surface of the second semiconductor layer 228. To thisend, the recesses 226 may be provided in the upper layer 224 of thefirst semiconductor layer 220. The recesses 226 may be formed bydepressing regions excluding regions where the first ohmic electrodes232 are formed on the upper layer 224. Thus, the upper layer 224 mayhave an upward protruded structure formed on the upper layer 224(hereinafter, referred to as “protrusions 225”), and the first ohmicelectrodes 232 may be disposed on the protrusions 225.

In the semiconductor device 200 with the same structure, each of thefirst ohmic electrodes 232 is bonded to the second semiconductor layer228 in the central region A1 to thereby come into ohmic contact witheach other. The second ohmic electrode 234 is bonded to the upper layer224 in the edge regions A2 to thereby come into ohmic contact with eachother. The Schottky electrode part 240 is bonded to each of the firstohmic electrodes 232 and the upper layer 224 of the central region A1 tothereby come into Schottky contact with one another. Also, the Schottkyelectrode part 240 may be used as an anode electrode, and the secondohmic electrode 234 may be used as a cathode electrode.

Meanwhile, the ohmic electrode part 230 and the Schottky electrode part240 may be formed of various materials. For example, the first ohmicelectrodes 232 and the second ohmic electrode 234 may be formed of thesame metallic material, and the Schottky electrode part 240 may beformed of metallic material different from those of the first and secondohmic electrodes 232 and 234. For example, the first and second ohmicelectrodes 232 and 234 may be formed of a metallic material composed ofat least one metal element of Al, Mo, Au, Ni, Pt, Ti, Pd, Ir, Rh, Co, W,Ta, Cu, and Zn. On the contrary, the Schottky electrode part 240 may beformed of a material composed of one or more metal elements differentfrom that of the ohmic electrode part 230.

Continuously, a detailed description will be given of various operationstates of the semiconductor device 200 in accordance with otherembodiment of the present invention having been described with referenceto FIGS. 11 and 12.

FIGS. 13A to 13C are views showing operation states of the semiconductordevice shown in FIGS. 11 and 12, respectively.

FIG. 13A is a view showing an operation state of the semiconductordevice when driven at a forward voltage equal to or higher than anon-voltage of the Schottky diode. Referring to FIG. 13A, when thesemiconductor device 200 in accordance with other embodiment of thepresent invention is driven at a first forward voltage equal to orhigher than the on-voltage of the Schottky diode, a depletion region(DR1) generated where the first semiconductor layer 220 and the Schottkyelectrode part 240 are joined together may be relatively reduced. Thus,in the semiconductor device 200, a current may flow through a firstcurrent path CP1 and a second current path CP2, wherein the firstcurrent path CP1 passes through the firs semiconductor layer 220 fromthe second bonding portions 244 of the Schottky electrode part 240, andthe second current path CP2 passes through the first and secondsemiconductor layers 220 and 228 from the first ohmic electrodes 232. Inthis case, since forward currents of the semiconductor device 200 areincreased, it is possible to operate the semiconductor device 200 evenat a low on-voltage.

FIG. 13B is a view showing an operation state of the semiconductordevice when driven at a forward voltage lower than an on-voltage of theSchottky diode. Referring to FIG. 13B, when the semiconductor device 200in accordance with other embodiment of the present invention is drivenat a second forward voltage lower than the on-voltage of the Schottkydiode, a depletion region DR2 generated where the second semiconductorlayer 220 and the Schottky electrode part 240 are joined together may bemore expanded than a case where the semiconductor device 100 is drivenat the first forward voltage as described in FIG. 13A. Such the expandeddepletion region DR2 may be wide enough to block a current flow betweenthe first semiconductor layer 220 and the Schottky electrode part 240.However, the second forward voltage may be controlled such that thedepletion region DR2 fails to block the second current path CP2. Thus,in the semiconductor device 200, a current may flow through the secondcurrent path CP2 alone.

FIG. 13C is a view showing an operation state of the semiconductordevice when driven at a reverse voltage. Referring to FIG. 13C, when thesemiconductor device 200 is driven at the reverse voltage, a depletionregion D3 may be more expanded to block the first and second currentpaths, indicated by reference numerals CP1 and CP2 of FIG. 13A, incomparison with the depletion region DR2 shown in FIG. 13B. Such thedepletion region DR3 blocks all current flows passing through the firstand second current paths CP1 and the CP2.

As described above, when the semiconductor device 100 is driven in theforward direction, a current may flow to the second ohmic electrode 234by the first ohmic electrodes 232 positioned below the Schottkyelectrode part 140 even in a state where the driving voltage is lowerthan the on-voltage of the Schottky diode, simultaneously while thecurrent may flow through the first ohmic electrodes 132 and the Schottkyelectrode part 140 in a state where the driving voltage is higher thanthe on-voltage of the Schottky diode. Thus, since the semiconductordevice 200 may increase forward currents, it can be operated even at alow driving voltage. Also, when the semiconductor device 200 is drivenin the reverse direction, the depletion region DR3 generated by theSchottky electrode part 140 allows the 2DEG to be disconnected, therebystably blocking a current flow.

Hereinafter, a description will be given of a method for manufacturingthe semiconductor device in accordance with other embodiment of thepresent invention. Herein, the repeated description for thesemiconductor device associated with embodiments illustrated withreference to FIGS. 11 and 12 will be omitted or simplified.

FIGS. 14A to 14D are views showing methods for manufacturing thesemiconductor device in accordance with other embodiment of the presentinvention, respectively.

Referring to FIG. 14A, the base substrate 210 may be prepared. A step ofpreparing the base substrate 210 may include a step of preparing asemiconductor substrate. The step of preparing the pre-base substrate210 may include a step of preparing at least one of a silicon substrate,a silicon carbide substrate, and a sapphire substrate.

A first semiconductor layer 220, a second semiconductor formation film227, and a first metal film 219 may be sequentially formed on the frontsurface of the pre-base substrate 210. The step of forming the firstsemiconductor layer 220 may include a step of forming a lower layer 222on the pre-base substrate 210, and a step of forming an upper layer 224on the lower layer 222. A step of forming the second semiconductorformation layer 227 may include a step of forming the semiconductor filmhaving a relatively higher impurity concentration than that of the upperlayer 224, on the pre-base substrate 210. For example, the step offorming the first semiconductor layer 220 may be achieved byepitaxial-growing the lower layer 222 by using the base substrate 212 asa seed layer, and then epitaxial-growing the upper layer 224 by usingthe lower layer 222 as a seed layer. Also, the step of forming thesecond semiconductor formation film 227 may be achieved by performing anepitaxial-growth process that uses the upper layer 224 as a seed layer.As for an epitaxial growth process for forming the first semiconductorlayer 220 and the second semiconductor formation layer 227, at least oneof a molecular beam epitaxial growth process, an atomic layer epitaxialgrowth process, a flow modulation organometallic vapor phase epitaxialgrowth process, a flow modulation organometallic vapor phase epitaxialgrowth process, and a hybrid vapor phase epitaxial growth process may beused. Furthermore, as for another process for forming the firstsemiconductor layer 220 and the second semiconductor formation layer227, any one of a chemical vapor deposition process and a physical vapordeposition process may be used.

The first photoresist pattern PR1 for exposing a partial region of thefirst metal film 219 may be formed on the first metal film 219. Thefirst photoresist pattern PR1 can expose the first metal film 219 onregions where the first ohmic electrodes, indicated by reference numeral232 of FIG. 14B, and edge regions A2 in the central region A1 of thepre-base substrate 210.

Referring to FIG. 14B, the first ohmic electrodes 232 and the secondsemiconductor layer 228 may be formed. In a step of forming the firstohmic electrodes 232 and the second semiconductor layer 228, recesses226 for exposing the upper layer 224 of the first semiconductor layer220 may be formed by using the first photoresist pattern PR1 as anetching mask. Thus, on the first semiconductor layer 220, theprotrusions 225 extended upward from the upper layer 224, and the firstohmic electrodes 232 disposed on the protrusions 225 may be formed.Herein, the protrusions 225 and the first ohmic electrodes 232 may beformed in a lattice configuration.

Referring to FIG. 14C, by removing a partial region of the pre-basesubstrate 210, the base substrate 212 may be formed. A step of formingthe base substrate 212 may include a step of forming the secondphotoresist pattern PR2 for exposing the central region A1 of the rearsurface of the pre-base substrate 210, and a step of forming the secondrecesses 212 a for exposing the rear surface 222 b of the lower layer222 of the first semiconductor layer 220 by using the second photoresistpattern PR2 as an etching mask.

Referring to FIG. 14D, on the rear surface 222 b of the firstsemiconductor layer 222, the second ohmic electrode 134 may be formed. Astep of forming the second ohmic electrode 134 may include a step offorming the second metal film buried in the second recesses 212 a formedon the base substrate 212. The second metal film may be a metal filmwith the same material as the first metal film for formation of thefirst ohmic electrodes 132. Also, the Schottky electrode part 140 may beformed. A step of forming the Schottky electrode part 140 may include astep of forming a third metal film which covers the first ohmicelectrodes 132, on the front surface of the first semiconductor layer220. The third metal film may be a metal film with a material differentfrom that of the first and second metal films. Thus, on the frontsurface of the base substrate 212, the Schottky electrode part 240 has aprominence and depression structure in which it is engaged with thefirst ohmic electrodes 232 and the second ohmic electrode 234 may beformed on the rear surface of the base substrate 212.

Hereinafter, a description will be given of various modified examples ofthe semiconductor device in accordance with other embodiment of thepresent invention. The repeated description for the same componentsbetween the above-described semiconductor device and semiconductordevices in accordance with various modified embodiments will be omittedor simplified. Since those skilled in the art can analogize operationprocesses of the modified examples to be described from the operationstates of the semiconductor device having been described with referenceto FIGS. 13A and 13C, the description for operation processes of themodified examples will be omitted. Also, since those skilled in the artcan analogize manufacturing methods of the modified examples to bedescribed from the manufacturing methods of the semiconductor devicehaving been described with reference to FIGS. 14A and 14D, thedescription for manufacturing methods of the modified examples will beomitted.

FIG. 15 is a view showing one modified example of the semiconductordevice in accordance with other embodiment of the present invention.Referring to FIG. 15, the semiconductor device 200 a may include a basesubstrate 212, a first semiconductor layer 220, an ohmic electrode part230 a, and a Schottky electrode part 240 a. The first semiconductorlayer 220 may include an upper layer 224 and a lower layer 222sequentially stacked on the front surface of the base substrate 212,wherein the upper layer 224 has a lower impurity concentration than thatof the lower layer 222. On the top surface of the upper layer 224, aplurality of protrusions 225 is formed. On the protrusions 225, thesecond semiconductor layer 228 having a higher impurity concentrationthan that of the upper layer 224 may be disposed. The ohmic electrodepart 230 a may be disposed on the rear surface 212 a of the firstsemiconductor layer 200. In addition, the ohmic electrode part 230 a maybe disposed in such a manner to be bonded to the rear surface 212 a inthe recesses 212 a formed on the base substrate 212. The Schottkyelectrode part 240 a may be formed to cover all surface of the firstsemiconductor layer 220, thereby achieving a prominence and depressionstructure in which it is engaged with the protrusions 225.

In the semiconductor device 200 a with the same structure, the Schottkyelectrode part 240 a may have first bonding portions 242 a bonded to thesecond semiconductor layer 228, and second bonding portions 244 a bondedto the upper layer 224 of the first semiconductor layer 220. Herein, thefirst bonding portions 242 a come into ohmic contact with the secondsemiconductor layer 228, and the second bonding portions 244 a come intoSchottky contact with the upper layer 224 of the first semiconductorlayer 220. The semiconductor device 200 a having the same structure mayhave a structure in which there is no separate ohmic electrode withinthe Schottky electrode part 140 d (e.g., first ohmic electrodes 232 ofFIG. 12). Thus, it is not necessary to perform a separate process forformation of ohmic electrodes within the Schottky electrode part 140 d.

FIG. 16 is a view showing another modified example of the semiconductordevice in accordance with other embodiment of the present invention.FIG. 17 is a cross-sectional view taken along a line IV-IV′ shown inFIG. 16.

Referring to FIGS. 16 and 17, the semiconductor device 200 b may includea base substrate 212, a first semiconductor layer 220, an ohmicelectrode part 230 b, and a Schottky electrode part 240. The firstsemiconductor layer 220 may include an upper layer 224 and a lower layer222 sequentially stacked on the front surface of the base substrate 212,wherein the upper layer 224 has a lower impurity concentration than thatof the lower layer 222. On the top surface of the upper layer 224, aplurality of protrusions 225 is formed. On the protrusions 225, thesecond semiconductor layer 228 having a higher impurity concentrationthan that of the upper layer 224 may be disposed. The ohmic electrodepart 230 b may be disposed on the rear surface 222 a of the firstsemiconductor layer 200. In addition, the ohmic electrode part 230 b maybe disposed in such a manner to be bonded to the rear surface 222 a inthe recesses 212 a formed on the base substrate 212. The Schottkyelectrode part 240 may be formed to cover all surface of the firstsemiconductor layer 220, thereby achieving a prominence and depressionstructure in which it is engaged with the protrusions 225. Meanwhile,the first and second ohmic electrodes 232 a and 234 a may have a ringshape based on the center 211 of the semiconductor layer 210. Forexample, the first and second ohmic electrodes 232 a and 234 a may havea ring shape sharing the center 111 and have diameters bigger than thoseof the first ohmic electrodes 232 a. Thus, the first and second ohmicelectrodes 232 a and 234 a may be formed in an annual ring configurationon the semiconductor layer 220.

In the case where the semiconductor device of the present invention isdriven in a forward direction, when a driving voltage is higher than anon-voltage of the Schottky diode, a current flows through an ohmicelectrode and Schottky electrode part at the same time. Further, acurrent flow by the first ohmic electrode positioned below the Schottkyelectrode part even if the driving voltage is lower than the on-voltageof the Schottky diode. Therefore, in the semiconductor device, forwardcurrents are increased, and thus it is possible to perform operationeven at a low driving voltage.

When the semiconductor device of the present invention is driven in areverse direction, a 2DEG is allowed to be disconnected by a depletionregion generated by the Schottky electrode part to thereby stably blocka current flow, which results in high reverse breakdown voltage.

In a method for manufacturing the semiconductor device, forward currentsare increased and reverse leakage currents are reduced, so that it ispossible to improve power converting efficiency of the semiconductordevice, as well as operation speed of the semiconductor device.

As described above, although the preferable embodiments of the presentinvention have been shown and described, it will be appreciated by thoseskilled in the art that substitutions, modifications and variations maybe made in these embodiments without departing from the principles andspirit of the general inventive concept, the scope of which is definedin the appended claims and their equivalents.

1. A semiconductor device comprising: a base substrate; a firstsemiconductor layer disposed on the base substrate; first ohmicelectrodes disposed on a central region of the first semiconductorlayer; a second ohmic electrode having a ring shape surrounding thefirst ohmic electrodes, on edge regions of the first semiconductorlayer; a second semiconductor layer interposed between the first ohmicelectrodes and the first semiconductor layer; and a Schottky electrodepart which covers the first ohmic electrodes on the central region, andis spaced apart from the second ohmic electrode.
 2. The semiconductordevice of claim 1, wherein the first ohmic electrode has a plurality ofohmic contact pillars with an island-shaped cross section, and theSchottky electrode part and the ohmic contact pillars are formed to bein a prominence and depression structure in which they are engaged withone another up and down.
 3. The semiconductor device of claim 1, whereinthe first ohmic electrode includes a plurality of ohmic contact pillarswith an island-shaped cross section, and the ohmic contacts are disposedto be in a grid configuration within the Schottky electrode part.
 4. Thesemiconductor device of claim 1, wherein the first ohmic electrodeincludes at least one electrode with a ring-shaped cross section.
 5. Thesemiconductor device of claim 4, wherein the first ohmic electrodeshares a center of the semiconductor layer, and includes first andsecond electrodes with mutually different diameters.
 6. Thesemiconductor device of claim 1, wherein the first ohmic electrodes areformed of the same metallic material as the Schottky electrode part, andthe Schottky electrode part comprises: first bonding portions bonded tothe second semiconductor layer to thereby come into ohmic contact withthe second semiconductor layer, and second bonding portions bonded tothe first semiconductor layer to thereby come into Schottky contact withthe first semiconductor layer.
 7. The semiconductor device of claim 1,wherein the first semiconductor layer comprises protrusions protrudedupward, and the second semiconductor layer is disposed on theprotrusions.
 8. The semiconductor device of claim 1, wherein the firstsemiconductor layer comprises: a lower layer adjacent to the basesubstrate; and an upper layer having a lower impurity concentration thanthat of the lower layer, and the second semiconductor layer has a higherimpurity concentration than that of the upper layer.
 9. Thesemiconductor device of claim 1, wherein the first ohmic electrodes arebonded to the second semiconductor layer on the central region tothereby come into ohmic contact with the second semiconductor layer, thesecond ohmic electrode is bonded to the semiconductor layer on the edgeregions to thereby come into ohmic contact with the semiconductor layer,and the Schottky electrode part is bonded to the second semiconductorlayer around the first ohmic electrodes to thereby come into Schottkycontact with the second semiconductor layer.
 10. The semiconductordevice of claim 1, wherein the Schottky electrode part is extended toinside of the semiconductor layer, and the Schottky electrode part has abottom surface with a height lower than that of the top surface of thesecond semiconductor layer.
 11. The semiconductor device of claim 1,wherein the second ohmic electrode is extended to inside of the firstsemiconductor layer.
 12. The semiconductor device of claim 1, furthercomprising a field plate disposed between the first ohmic electrodes andthe second ohmic electrode.
 13. The semiconductor device of claim 11,wherein internal side portions of the filed plate are covered by theSchottky electrode, and the external side portions of the filed platepartially cover an internal side of the top part of the second ohmicelectrode, and central portion of the field plate is exposed.
 14. Asemiconductor device comprising: a base substrate; a first semiconductorlayer disposed on the base substrate; first ohmic electrodes which aredisposed on a central region of the first semiconductor layer and have aplurality of ohmic contact pillars with an island-shaped cross section;a second ohmic electrode disposed on the edge regions of the firstsemiconductor layer; and a Schottky electrode part which includes firstbonding portions bonded to the first ohmic contact pillars and secondbonding portions bonded to the first semiconductor layer, wherein adepletion region is provided to permit or to block a current flow to thesecond ohmic electrode from the first ohmic electrodes and the Schottkyelectrode part, the depletion region being generated within the firstsemiconductor layer when the semiconductor layer is bonded to the secondbonding portions.
 15. The semiconductor device of claim 14, wherein theSchottky electrode part is engaged with the first ohmic contact pillarsto thereby achieve a prominence and depression structure.
 16. Thesemiconductor device of claim 14, wherein, when the semiconductor deviceis driven at a forward voltage equal to or higher than an on-voltage ofthe Schottky diode, the depletion region is provided to permit a currentflow to the second ohmic electrode from the Schottky electrode part andthe first ohmic electrodes.
 17. The semiconductor device of claim 14,wherein, when the semiconductor device is driven at a forward voltagelower than the on-voltage of the Schottky diode, the depletion region isprovided to block a current flow to the second ohmic electrode from theSchottky electrode part.
 18. The semiconductor device of claim 14,wherein, when the semiconductor device is driven at a reverse voltage,the depletion region is provided to block a current flow to the secondohmic electrode from the Schottky electrode part and the first ohmicelectrodes.
 19. A method for manufacturing a semiconductor devicecomprising: preparing a base substrate; forming a first semiconductorlayer on the base substrate; forming a second semiconductor layer on apartial region of the first semiconductor layer; forming first ohmicelectrodes on a top part of the second semiconductor layer; forming asecond ohmic electrode surrounding the first ohmic electrodes on edgeregions of the first semiconductor layer; and forming a Schottkyelectrode part which covers the first ohmic electrodes on the centralregion of the semiconductor layer.
 20. The method of claim 19, whereinforming the first ohmic electrodes comprises forming a plurality ofohmic contact pillars with an island-shaped cross section, and the ohmiccontact pillars have recesses formed on regions remaining afterexcluding regions of the first semiconductor layer where the first ohmicelectrodes are to be formed.
 21. The method of claim 19, wherein formingthe first ohmic electrodes comprises forming the first and secondelectrodes provided to be in an annual ring configuration on the firstsemiconductor layer, and the first and second electrodes have recessesformed on regions, remaining after excluding regions of the firstsemiconductor layer where the first ohmic electrodes are to be formed.22. The method of claim 20, wherein the recess has a bottom surface witha height lower than that of the bottom surface of the secondsemiconductor layer.
 23. The method of claim 19, wherein forming thefirst semiconductor layer comprises: forming a lower layer having a highimpurity concentration on the base substrate; and forming an upper layerhaving an impurity concentration lower than that of the lower layer, andforming the second semiconductor layer comprises forming a semiconductorfilm having an impurity concentration higher than that of the upperlayer.
 24. The method of claim 23, wherein forming the upper layercomprises: performing an epitaxial-growth process which uses the lowerlayer as a seed layer, and forming the second semiconductor layercomprises a step of performing any one of an epitaxial-growth processwhich uses the upper layer as a seed layer, and a deposition process.25. The method of claim 19, further comprising forming a field plate onthe first semiconductor layer between the Schottky electrode part andthe second ohmic electrode.
 26. The method of claim 25, wherein formingthe second ohmic electrode comprises a step of forming a metal film,which has external side portions partially covering a top part of thesecond ohmic electrode and a part of internal side portions covered bythe Schottky electrode part.